DESCRIPTION: (Adapted from the Applicant's Abstract.) Recent neurophysiological and behavioral experiments strongly suggest that the capacity for rapid and effective spatial orientation is based primarily on the interaction between a set of high-order neurons that transmit a representation of spatial location, and an extensive network of neocortical and subcortical neurons which use vestibular, angular-velocity information to compute and transmit a signal reflecting the azimuthal component of the animal's head orientation, relative to an inertial reference framework. Such a system is ideally suited for the computation of relevant behavioral trajectories in an earth-bound environment, first because it enables space to be internally represented and stored economically as a set of landmark- vectors, and second, because it enables the trajectory computation to be carried out by vector subtraction. The latter capacity permits the rapid calculation of novel, direct trajectories to a desired target. Clearly, the fact that this orientation system is based on azimuthal information with respect to the local gravitational field suggests that problems may develop in low or zero-gravity situations. The present proposal for the NeuroLab mission aims to use neurophysiological experiments in freely behaving rodents to address the question of how this crucial system performs and adapts to low gravity conditions. Methods developed in this laboratory have enabled the simultaneous recording from large numbers of neurons involved in the spatial orientation system and which enable the same neuronal ensembles to be studied over periods of up to several weeks. This technology will maximize the amount of relevant neurophysiological data that can be obtained from a small number of rodents (2-4). The investigators realistically expect to be able to obtain well isolated unit recordings from as many as 1000 neocortical, thalamic, and tectal neurons over the course of a single mission, and to study the ensemble interactions of 50-150 cells in any given recording experiment. They also propose to assist and collaborate with other research groups in employing the same technology to address other important neurophysiological questions of relevance to space flight, including possible changes in motor control and sensori-motor integration, sleep-waking cycles, and autonomic control.